Roller bearing

ABSTRACT

A roller bearing capable of effectively restraining occurrence of smearing or the like is provided. A cylindrical roller bearing includes: an outer ring having an outer ring raceway surface; an inner ring having an inner ring raceway surface that faces the outer ring raceway surface; and a plurality of cylindrical rollers rollably disposed between the outer ring raceway surface and the inner ring raceway surface. The inner ring raceway surface of the inner ring is provided with a manganese phosphate coating, and a rolling contact surface of each cylindrical roller is provided with a diamond-like carbon coating.

TECHNICAL FIELD

The invention relates to a roller bearing for use in a wind-poweredgenerator or the like.

BACKGROUND ART

As bearings disposed in, for example, gear boxes for wind-poweredgeneration, medium-size roller bearings are often used. There are somecases where a windmill for use in wind-powered generation is placed in anon-steady operation which is other than a normal power-generatingoperation and in which rotary torque is not transmitted to a speedincreaser, when electric power is cut off due to electricity outage orthe like, when a control of reducing the rotary torque is performed dueto high wind or the like, etc. In such a case, especially, a rollerbearing mounted on a high-speed shaft rotates at a high speed in anearly non-load state, so that a raceway surface of the bearing is notsupplied with sufficient lubricant and therefore smearing (a phenomenonin which a plurality of minute seizures is generated) occurs on araceway surface of a rotary ring or rolling contact surfaces of rollers,resulting in a reduced service life of the roller bearing.

Therefore, conventionally, in order to protect the raceway surface ofthe rotary ring and the rolling contact surfaces of the rollers, theraceway surface and the rolling contact surfaces are subjected to asurface treatment with manganese phosphate coating (see, for example,Patent Document 1).

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent Application Publication No.2003-156053

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

However, the manganese phosphate coating is inferior in load bearing,and therefore has a problem that peeling easily occurs on the racewaysurface or the rolling contact surfaces. In order to solve this problem,it is conceivable to form a diamond-like carbon (DLC) coating that isexcellent in load bearing, instead of the manganese phosphate coating,on the raceway surface or the like. However, in this case, the frictioncoefficient is smaller, and therefore there occurs a problem thatslippage more easily occurs between the raceway surface of the rotaryring and the rolling contact surfaces of the rollers and, therefore,occurrence of smearing cannot be sufficiently restrained.

The invention has been made in view of the foregoing circumstances, andit is an object of the invention to provide a roller bearing capable ofeffectively restraining occurrence of smearing or the like.

Means for Solving the Problem

The roller bearing of the invention for achieving the foregoing objectis characterized by comprising: a fixed ring having a fixed racewaysurface; a rotary ring having a rotary raceway surface that faces thefixed raceway surface; and a plurality of rollers rollably disposedbetween the fixed raceway surface and the rotary raceway surface,wherein, out of the rotary raceway surface and a rolling contact surfaceof each of the rollers, one of the surfaces is provided with a manganesephosphate coating and the other surface is provided with a diamond-likecarbon coating.

According to the invention, out of the rotary raceway surface of therotary ring and the rolling contact surface of each roller, one of thesurfaces is provided with a manganese phosphate coating that is inferiorin load bearing but greater in friction coefficient, and the othersurface is provided with a diamond-like carbon coating that is small infriction coefficient but excellent in load bearing. That is, since therotary raceway ring and each rolling contact surface are provided withtwo kinds of coatings that cover each other's shortcomings, themanganese phosphate coating that is great in friction coefficient makesslippage between the rotary raceway surface and the rolling contactsurface of each roller less likely to occur, so that occurrence ofsmearing can be effectively restrained. Furthermore, since thediamond-like carbon coating which is excellent in load bearing hardensthe surface, occurrence of peeling on the surface provided with thecoating can be effectively restrained.

Furthermore, it is preferable that, in the roller bearing, the one ofthe surfaces be the rotary raceway surface and the other surface be therolling contact surface of each roller.

In this case, since the rotary raceway surface is provided with themanganese phosphate coating, which is great in friction coefficient, thefriction force on the coating makes it possible to efficiently transmitrotary drive force of the rotary ring to the rollers.

Furthermore, it is preferable that, on the rotary ring, a rib surfacethat is in sliding contact with an end surface of each roller beprovided on at least one side of the rotary raceway surface in an axialdirection, and that, out of the rib surface and the end surface of eachroller, one of the surfaces be provided with the manganese phosphatecoating and the other surface be provided with the diamond-like carboncoating.

In this case, since the rib surface of the rotary ring and the endsurface of each roller are also provided with two kinds of coatings thatcover each other's shortcomings, due to the manganese phosphate coating,which is great in friction coefficient, the rollers are more likely tobe rotated together with the rotary ring by the sliding contactresistance between the rib surface and the end surface, so that rotarydrive force of the rotary ring can be more efficiently transmitted tothe rollers. Furthermore, since the diamond-like carbon coating, whichis excellent in load bearing, hardens the surface, occurrence of peelingon the surface provided with the coating can be effectively restrained.

Effects of the Invention

According to the roller bearing of the invention, it is possible toeffectively restrain occurrence of smearing or the like by performing asurface treatment with coating, thereby increasing the service life.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is sectional view showing a roller bearing according to a firstembodiment of the invention.

FIG. 2 is a graph showing results of an endurance test of coatings.

FIG. 1 is a schematic diagram showing a testing device for theaforementioned endurance test.

FIG. 4 is a graph showing transitions in friction coefficients ofcoatings.

FIG. 5 is a schematic diagram showing a measuring device for measuringtransitions in the friction coefficients.

FIG. 6 is a sectional view showing a roller bearing according to asecond embodiment of the invention.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the roller bearing according to theinvention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a roller bearing according to a firstembodiment of the invention. The roller bearing according to the presentembodiment is a cylindrical roller bearing 1 that bears a radial load ina gearbox for wind-powered generation. The cylindrical roller bearing 1includes an outer ring 2 as a fixed ring, an inner ring 3 as a rotaryring that is disposed so as to be rotatable coaxially with the outerring 2, a plurality of cylindrical rollers 4 that are rollably disposedbetween the outer ring 2 and the inner ring 3, and a cage 5 for holdingthe cylindrical rollers 4 at predetermined intervals in circumferentialdirection.

The outer ring 2 has an outer ring raceway surface (fixed racewaysurface) 2 a that is formed on its inner periphery, and rib portions 2 bformed to be protruded radially inward at axially opposite sides of theouter ring raceway surface 2 a. Each rib portion 2 b has a rib surface 2b 1 that is in sliding contact with a corresponding one of end surfaces4 b of each cylindrical roller 4 at the axially opposite sides thereof.

On the outer periphery of the inner ring 3, there is formed an innerring raceway surface (rotary raceway surface) 3 a that faces the outerring raceway surface 2 a of the outer ring 2. The cylindrical rollers 4are rollably disposed between the outer ring raceway surface 2 a and theinner ring raceway surface 3 a. An outer peripheral surface of each ofthe cylindrical rollers 4 is a rolling contact surface 4 a that rolls onthe outer ring raceway surface 2 a and the inner ring raceway surface 3a.

The cage 5 includes a first annular portion 5 a and a second annularportion 5 b that are disposed apart from each other in the axialdirection, and a plurality of pillar portions 5 c that are disposed atequal intervals in the circumferential direction of the two annularportions 5 a, 5 b and that connect the two annular portions 5 a, 5 b.Pockets 5 d are formed between the two annular portions 5 a, 5 b and theadjacent pillar portions 5 c. The cylindrical rollers 4 are disposed inthese pockets 5 d. The cage 5 retains, in the plurality of pockets 5 d,the plurality of cylindrical rollers 4 at predetermined intervals in thecircumferential direction.

The outer ring raceway surface 2 a of the outer ring 2, the inner ringraceway surface 3 a of the inner ring 3 and the rolling contact surface4 a of each of the cylindrical rollers 4 are surface-treated withrespectively different coatings. Specifically, on each of the outer ringraceway surface 2 a and the inner ring raceway surface 3 a, there isformed a manganese phosphate coating 6 a that extends over the entirecircumference of the raceway surface. Furthermore, on the rollingcontact surface 4 a of each cylindrical roller 4, there is formed adiamond-like carbon (DLC) coating 6 b that contains, for example,tungsten carbide carbon (WCC) and that extends over the entirecircumference of the roller. The film thickness of each manganesephosphate coating 6 a and each diamond-like carbon coating 6 b is setequal to or less than 3 μm.

FIG. 2 is a graph showing results of an endurance test that wasconducted until occurrence of peeling of the manganese phosphate coatingand the diamond-like carbon coating.

Conditions of this endurance test are as follows. A first test piece isa test piece in which a manganese phosphate coating is formed on aflat-plate test piece made of JIS SUJ2. Furthermore, a second test pieceis a test piece in which a diamond-like carbon coating is formed on aflat-plate test piece made of JIS SUJ2.

A method of the endurance test performed until peeling occurred on themanganese phosphate coating of the first test piece will be shown below.

FIG. 3 is a schematic diagram of a testing device for the endurancetest. This testing device includes an inner ring 21 for an axial bearingwhich is made of JIS SUJ2 and which has an annular raceway 21 a, sixballs 22 of ⅜ inch made of JIS SUJ2, an annular cage 23 that holds eachof the balls 22, lubricating oil 24, and a container 25 in which thefirst test piece 30 is disposed and the lubricating oil 24 is stored.The annular raceway's diameter (the diameter of a groove bottom of theraceway 21 a, P.C.D.) is φ38 mm.

The first test piece 30 was placed in the container 25 so that themanganese phosphate coating 31 (corresponding to the manganese phosphatecoating 6 a according to the invention) faced upward in the verticaldirection, and the six balls 22 held by the cage 23 were placed on themanganese phosphate coating 31, and the inner ring 21 was put on the sixballs 22 so that the balls 22 were placed within the raceway 21 a. Thelubricating oil 24 was put into the container 25 so that the first testpiece 30 was completely submerged and the cage 23 was immersed up to itssubstantially middle position in the vertical direction. As thelubricating oil 24, MEROPA WM320 in trade name (produced by Chevron) wasused. Axial load in the direction of an arrow A shown in the drawing wasapplied between the first test piece 30 and the inner ring 21 so thatthe contact surface pressure between the balls 22 and the first testpiece 30 became equal to a predetermined value, and then the first testpiece 30 was immobilized and the inner ring 21 was rotated at a rotationspeed of 1200 min⁻¹. The passage speed of the balls 22 at this time was3600 min⁻¹.

In the endurance test, as shown in FIG. 2, the contact surface pressurewas intermittently raised so as to be 2.0 GPa at step S1, 2.6 GPa atstep S2, 3.1 GPa at step S3, 3.5 GPa at step S4, and 4.1 GPa at step S5.At steps S1 to S5, the inner ring 21 was rotated 1×10⁷ times.

A method for the endurance test performed until peeling occurred on thediamond-like carbon coating of the second test piece will be shownbelow.

As shown in FIG. 3, in the testing device used for the endurance testperformed until peeling occurred on the manganese phosphate coating 31mentioned above, the test was conducted by using the second test piece40 instead of the first test piece 30 as a test piece. That is, thesecond test piece 40 was placed in the container 25 so that thediamond-like carbon coating 41 (corresponding to the diamond-like carboncoating 6 b according to the invention) faced upward in the verticaldirection, and the six balls 22 held by the cage 23 were placed on thediamond-like carbon coating 41, and then a test similar to the test ofthe first test piece 30 was conducted.

In FIG. 2, with regard to the manganese phosphate coating, peelingoccurred when the contact surface pressure was 3.1 GPa, whereas, withregard to the diamond-like carbon coating, peeling occurred when thecontact surface pressure was 4.1 GPa. From results of this test, it canbe understood that the diamond-like carbon coating is more excellent inload bearing than the manganese phosphate coating.

FIG. 4 is a graph showing transitions in friction coefficients of themanganese phosphate coating and the diamond-like carbon coating under ano-lubricant condition.

A measurement method for the friction coefficients is as follows. Athird test piece is a test piece in which a manganese phosphate coatingis formed in a flat-plate test piece made of JIS SUJ2. Furthermore, afourth test piece is a test piece in which a diamond-like carbon coatingis formed on a flat-plate test piece made of JIS SUJ2.

A measurement method for transitions in the friction coefficient of themanganese phosphate coating of the third test piece will next be shown.

FIG. 5 is a schematic diagram showing a measuring device for measuringtransitions in the friction coefficient. In this measuring device, balls51 of 3/16 inch made of JIS SUJ2 and lubricating oil (not shown) wereprepared.

A third test piece 60 was disposed so that a manganese phosphate coating61 (corresponding to the manganese phosphate coating 6 a according tothe invention) faced upward in the vertical direction, and the balls 51fixed so as not to roll were placed on the manganese phosphate coating61. Lubricating oil was applied to surface of the third test piece 60.As the lubricating oil, MEROPA WM320 in trade name (produced by Chevron)was used. An axial load of 10 N was applied between the third test piece60 and the balls 51 so that the contact surface pressure became equal to1.6 GPa. In this state, the balls 51 were moved relative to the thirdtest piece 60 over a distance of 10 mm at an average linear speed of 40mm/s. This relative movement was continued as reciprocal movement shownby arrows B in FIG. 5 for 3600 s.

A measurement method for transitions in the friction coefficient of thediamond-like carbon coating of the fourth test piece will next be shown.

As shown in FIG. 5, in the measuring device used in the measurementmethod for transitions in the friction coefficient of the manganesephosphate coating 61 described above, a test was conducted by using thefourth test piece 70 instead of the third test piece 60 as a test piece.That is, the fourth test piece 70 was placed so that the diamond-likecarbon coating 71 (corresponding to the diamond-like carbon coating 6 baccording to the invention) was in contact with the balls 51, and thenmeasurement similar to the measurement on the third test piece 60 wasconducted.

In FIG. 4, the friction coefficient of the manganese phosphate coatingtransitions in the range of 0.4 to 0.6, whereas the friction coefficientof the diamond-like carbon coating transitions below or at 0.2. Fromthis result, it can be understood that the manganese phosphate coatingis greater in friction coefficient than the diamond-like carbon coating.

With the cylindrical roller bearing 1 according to the embodiment of theinvention described above, out of the inner ring raceway surface 3 a ofthe inner ring 3, which is a rotary ring, and the rolling contactsurface 4 a of each cylindrical roller 4, one of the surfaces isprovided with the manganese phosphate coating 6 a that is inferior inload bearing but great in friction coefficient, and the other surface isprovided with the diamond-like carbon coating 6 b that is small infriction coefficient but excellent in load bearing. That is, on theinner ring raceway surface 3 a and the rolling contact surface 4 a,there are formed two kinds of coatings that cover each other'sshortcomings. Therefore, due to the manganese phosphate coating 6 a,which is great in friction coefficient, slippage is less likely to occurbetween the inner ring raceway surface 3 a and the rolling contactsurface 4 a, so that occurrence of smearing (a phenomenon in which aplurality of minute seizures is generated) can be effectivelyrestrained. Furthermore, the diamond-like carbon coating 6 b, which isexcellent in load bearing, hardens the surface, so that occurrence ofpeeling on the rolling contact surface 4 a provided with the coating 6 bcan be effectively restrained. Therefore, it becomes possible toincrease the service life of the cylindrical roller bearing 1.

Furthermore, since the manganese phosphate coating 6 a, which is greatin friction coefficient, is formed on the inner ring raceway surface 3a, the friction force of the manganese phosphate coating 6 a makes itpossible to efficiently transmit rotary drive force of the inner ring 3to the cylindrical rollers 4.

Note that, in the present embodiment, the rib surfaces 2 b 1 of theouter ring 2 as a fixed ring and the end surfaces 4 b of eachcylindrical roller 4 are not surface-treated with coating. Therefore,increase in the sliding contact resistance between the rib surfaces 2 b1 and the cylindrical rollers 4 due to coating can be prevented.

FIG. 6 is a sectional view showing a roller bearing according to asecond embodiment of the invention. The present embodiment differs fromthe first embodiment in that rib surfaces are formed on an inner ringand that the rib surfaces and the end surfaces of cylindrical rollersare surface-treated with coating.

In the present embodiment, the outer periphery of the inner ring 3 hasrib portions 3 b that are protruded radially outward at axially oppositesides of an inner ring raceway surface 3 a. Each rib portion 3 b has arib surface 3 b 1 that is in sliding contact with a corresponding one ofthe end surfaces 4 b of each cylindrical roller 4.

The rib surfaces 3 b 1 of the inner ring 3 and the end surfaces 4 b ofeach cylindrical roller 4 are surface-treated with respectivelydifferent coatings. Specifically, a manganese phosphate coating 6 a isformed entirely over each rib surface 3 b 1. Furthermore, a diamond-likecarbon (DLC) coating 6 b that contains, for example, a tungsten carbidecarbon (WCC) is formed entirely over each end surface 4 b. The filmthickness of each of the manganese phosphate coatings 6 a and thediamond-like carbon coatings 6 b is set equal to or less than 3 μm.

Similarly to the embodiment of the invention described above, since theinner ring raceway surface 3 a of the inner ring 3 and the rollingcontact surface 4 a of each cylindrical roller 4 are surface-treatedwith the manganese phosphate coating 6 a and the diamond-like carboncoating 6 b, respectively, occurrence of smearing or the like on theinner ring raceway surface 3 a and the rolling contact surface 4 a canbe effectively prevented, and therefore it becomes possible to increasethe service life of the cylindrical roller bearing 1.

Furthermore, since the rib surfaces 3 b 1 of the inner ring 3 and theend surfaces 4 b of each cylindrical roller 4 are provided with twokinds of coatings that cover each other's shortcomings, due to themanganese phosphate coating 6 a, which is great in friction coefficient,the cylindrical rollers 4 are more likely to be rotated together withthe inner ring 3 by the sliding contact resistance between the ribsurfaces 3 b 1 and the end surfaces 4 b of the cylindrical rollers 4, sothat rotary drive force of the inner ring 3 can be more efficientlytransmitted to the cylindrical rollers 4. Furthermore, since thediamond-like carbon coating 6 b, which is excellent in load bearing,hardens the surface, occurrence of peeling on the end surfaces 4 bprovided with the coatings 6 b can be effectively restrained.

Note that, the invention may be carried out with changes as appropriate,without being limited to the foregoing embodiments. For example,although in the foregoing embodiments, the manganese phosphate coatingis formed on each of the outer ring raceway surface and the inner ringraceway surface and the diamond-like carbon coating is formed on each ofthe rolling contact surfaces of the cylindrical rollers, thediamond-like carbon coating may be formed on each of the outer ringraceway surface and the inner ring raceway surface and the manganesephosphate coating may be formed on each of the rolling contact surfacesof the cylindrical rollers.

Furthermore, although in the foregoing embodiments, coating is formed oneach of the outer ring raceway surface and the inner ring racewaysurface, it is only necessary to form coating at least on an inner ringraceway surface of a rotary ring.

Furthermore, although in the second embodiment, the manganese phosphatecoating is formed on each rib surface and diamond-like carbon coating isformed on each of the end surfaces of the cylindrical rollers, thediamond-like carbon coating may be formed on each rib surface and themanganese phosphate coating may be formed on each of the end surfaces ofthe cylindrical rollers.

Furthermore although in the second embodiment, the diamond-like carboncoating is formed on each of the rolling contact surfaces and the endsurfaces of the cylindrical rollers, the diamond-like carbon coating ofthe rolling contact surface of a cylindrical roller may be continuouswith the diamond-like carbon coatings of the end surfaces of thecylindrical roller. Furthermore, a manganese phosphate coating may beformed on each of the rolling contact surfaces and the end surfaces ofthe cylindrical rollers. In this case, the manganese phosphate coatingof the rolling contact surface of a cylindrical roller may be continuouswith the manganese phosphate coating of the end surfaces of thecylindrical roller.

Furthermore, although in the second embodiment, a manganese phosphatecoating is formed on each of the inner ring raceway surface and the ribsurfaces of the inner ring, the manganese phosphate coating on the innerring raceway surface of the inner ring and the manganese phosphatecoating on each of the rib surfaces of the inner ring may be continuouswith each other. Furthermore, a diamond-like carbon coating may beformed on each of the inner ring raceway surface and the rib surfaces ofthe inner ring. In this case, the diamond-like carbon coating on theinner ring raceway surface of the inner ring and the diamond-like carboncoating on each of the rib surfaces of the inner ring may be continuouswith each other.

Furthermore, out of the diamond-like carbon coating and the manganesephosphate coating, one of the coatings may be formed on each of theinner ring raceway surface of the inner ring and the end surfaces of thecylindrical rollers, and the other coating may be formed on each of therib surfaces of the inner ring and the rolling contact surfaces of thecylindrical rollers.

Furthermore, although in the second embodiment, the coating is formedover the entire end surfaces of each cylindrical roller, it is onlynecessary to form coating on at least a portion that is in slidingcontact with a corresponding one of the rib surfaces.

Furthermore, although in each of the cylindrical roller bearings in theforegoing embodiments, the fixed ring is the outer ring, and the rotaryring is the inner ring, the fixed ring may be the inner ring and therotary ring may be the outer ring.

Furthermore, the roller bearing is not limited to a radial cylindricalroller bearing, but may also be a thrust roller bearing or a taperedroller bearing.

DESCRIPTION OF REFERENCE CHARACTERS 1: CYLINDRICAL ROLLER BEARING(ROLLER BEARING) 2: OUTER RING (FIXED RING)

2 a: OUTER RING RACEWAY SURFACE (FIXED RACEWAY SURFACE)2 b 1: RIB SURFACE

3: INNER RING (ROTARY RING)

3 a: INNER RING RACEWAY SURFACE (ROTARY RACEWAY SURFACE)3 b 1: RIB SURFACE

4: CYLINDRICAL ROLLER (ROLLER)

4 a: ROLLING CONTACT SURFACE4 b: END SURFACE6 a: MANGANESE PHOSPHATE COATING6 b: DIAMOND-LIKE CARBON COATING

1. A roller bearing, comprising: a fixed ring having a fixed racewaysurface; a rotary ring having a rotary raceway surface that faces thefixed raceway surface; and a plurality of rollers rollably disposedbetween the fixed raceway surface and the rotary raceway surface,wherein, out of the rotary raceway surface and a rolling contact surfaceof each of the rollers, one of the surfaces is provided with a manganesephosphate coating and the other surface is provided with a diamond-likecarbon coating.
 2. The roller bearing according to claim 1, wherein: theone of the surfaces is the rotary raceway surface; and the other surfaceis the rolling contact surface of each of the rollers.
 3. The rollerbearing according to claim 1, wherein: on the rotary ring, a rib surfacethat is in sliding contact with an end surface of each of the rollers isprovided on at least one side of the rotary raceway surface in an axialdirection; and out of the rib surface and the end surface of each of therollers, one of the surfaces is provided with the manganese phosphatecoating and the other surface is provided with the diamond-like carboncoating.
 4. The roller bearing according to claim 2, wherein: on therotary ring, a rib surface that is in sliding contact with an endsurface of each of the rollers is provided on at least one side of therotary raceway surface in an axial direction; and out of the rib surfaceand the end surface of each of the rollers, one of the surfaces isprovided with the manganese phosphate coating and the other surface isprovided with the diamond-like carbon coating.